Cesium, or caesiuma, is the chemical element with atomic number 55, symbol Cs.
Under standard conditions, the simple cesium body is a soft and ductile metal,
white or silver to golden. Its melting point (28 กใ C) is close to room
temperature and to the human body (CNTP), at which it can remain in the liquid
state by supercooling; cesium shares this property with gallium and rubidium,
mercury being the only pure liquid metal and evaporating at room temperature.
Cesium is the most alkaline of the alkali metals (strongest known base; enough
to attack glass). Its chemical properties are close to those of rubidium and
potassium, which belong to the same family. It reacts violently with water and
air (explosive reaction). It is extremely reactive and pyrophoric, and reacts
with water even at a temperature as low as -116 กใ C.
It is extracted from the pollucite (aluminosilicate Cs4Al4Si9O26 กค H2O) but it
is also present in trace amounts in lepidolite
Cesium is the least electronegative (most electropositive) of metals (apart from
francium, but the latter is radioactive with a short half-life), which makes it
interesting for the photoelectric effect9.
It has two degrees of oxidation: 0 (metal) and + I (ionic compounds) 9.
Its three main types of compounds are9:
halides (fluoride, chloride, bromide, iodide);
carbonate and hydroxide;
salts of organic acids (including formate).
Reactivity: cesium reacts violently with air (production of superoxide), with
water even frozen (explosion, which is inhibited only from −116 กใ C), with
phosphorus, sulfur and dichlor
409 isotopes of cesium are known, with a mass number varying between 112 and
151, plus 17 isomers. This number of isotopes is one of the records for a
chemical element9.
The only stable isotope is 133Cs (78 neutrons), which makes cesium a
monoisotopic element. This isotope being the only one present in nature, cesium
is also a mononucleidic element.
The other isotopes are radioactive and radiotoxic9. They are produced in
supernovae, and on Earth are the result of fallout from atmospheric nuclear
tests or nuclear accidents (Chernobyl disaster, for example) and nuclear waste,
notably cesium 137. Two isotopes, 134Cs (half-life two years) and 137Cs (gamma
emitter, half-life of 30 years) are fission products of uranium9, possible
tracers of leaks or accidents from nuclear reactors.
The most well-known radiogenic isotope 137Cs. It has indeed been widely used in
the hydrological and ecological studies implemented to evaluate the effects of
several general contamination of the atmosphere induced from 1945 by the use of
atomic bombs, then by nuclear tests, then (in the northern hemisphere mainly) by
the Chernobyl accident) and finally to a lesser extent, due to releases from
nuclear power plants or reprocessing sites, storage, etc. Its signature and
monitoring have, for example, made it possible to measure how quickly
groundwater is being renewed or to demonstrate that a cave was or was not
isolated from the outside world. It has also been used to study the
environmental kinetics of cesium (especially in the food chain). It has a
radioactive half-life of 30.15 years. It disintegrates into 137m barium, a short
period isomer (2.55 min) which disintegrates itself into stable 137 barium. Its
standard atomic mass is 132.9054519 (2) u.
Radioactive waste, fallout from atmospheric nuclear tests or the Chernobyl
accident may contain cesium 135 with a very long radioactive period, cesium 134
(2 year period), and cesium 137 (30 year period). Cesium 135 has a radioactive
period of 2.3 million years and is part of long-lived radioactive waste
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rhenium germanium zirconium cadmium hafnium
barium lithium beryllium strontium calcium
Tantalum gadolinium samarium yttrium ytterbium
Lutetium praseodymium holmium erbium thulium dysprosium
terbium europium lanthanum cerium neodymium scandium
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